1. Field of the Invention
The present invention relates to a transmission apparatus and a transmission method, and more specifically, to a technology capable of transmitting data more equally and efficiently in a case where the number of data distributions is limited.
2. Description of the Related Art
Recently, there has been utilized a technology in which multimedia data such as video and audio is streamed via an IP network in order to view the video and listen to the audio. More specifically, when distributing the multimedia data that requires real-time distribution, e.g., live video, a communication protocol, which is referred to as Real-time Transport Protocol (RTP), is generally used.
RTP is a protocol for transferring data, e.g., mainly audio and video, in real time and is defined as RFC3550 by Internet Engineering Task Force (IETF). RTP is an upper protocol of User Datagram Protocol (UDP), which is a non-connection type protocol. In a case where video or audio data is packetized by using RTP for communication, the RTP packet that streams through a network is generally referred to as stream data or a media stream.
Generally, Real Time Streaming Protocol (RTSP) is used as a protocol for controlling a communication session such as a start and an end of a media stream by using RTP. RTSP is defined as RFC 2326 by IETF. Japanese Patent Application Laid-open No. 2011-211390 discusses a technology for controlling a session by using RTSP and Session Initiation Protocol (SIP).
A server that conducts session control by using RTSP may sometimes limit the number of sessions connectable at a time. The number of sessions connectable at a time is limited because of, for example, an issue of a resource of the server which distributes stream data and an issue of a communication band of a network. In a case where the number of sessions by RTSP is limited by the server, a client's connection request, which is made after the number of sessions reaches the limit, is rejected by the server. In other words, a mechanism like a reservation system for a connection request is not present in communication control according to RTSP. Therefore, in an environment where the number of sessions is limited, a client who can access the server is generally determined on a first-come-first-served basis.
Generally, at a point of time when the client's connection request is rejected by the server, a session by RTSP between the server and the client who made the rejected request is to be disconnected. Therefore, the client cannot know the subsequent state of the server. Under the circumstance, however, if the number of sessions by RTSP falls below the upper limit number because of any change of the situation, the client who desires to establish a connection by RTSP can access the server if the client makes the connection request at that timing.
However, a client not actually in connection with the server cannot know the state of the server in real time. Therefore, in order to confirm whether the client can connect to the server, in some cases, the client may waste time in attempting to connect to the server many times or may miss a right timing to connect to the server.